iOS 7 to be available for installation from 18 September for free

iOS 7, billed as the "biggest change to iOS since the introduction of the iPhone", by Apple CEO Tim Cook, will be available from 18 September on iPhone, iPad and iPod for free.

The release date was confirmed by Craig Federighi, the senior vice president of software engineering at Apple's ongoing iPhone 5S and 5C launch event in California.

The new operating system was first unveiled at Apple's Worldwide Developer Conference on 10 June. Since then there has been a series of beta versions made available to developers, and advertising for the new software has been sprawled across the company's homepage throughout the summer.

Now, with the launch of two new iPhones today, which will run iOS 7 out of the box, the OS is set to be released to the public with iPhone 4 and above, iPad 2 and above, iPad mini and 5G iPod touch users able to install the latest software.

As well as a full user interface redesign, which is described by Apple as "completely new" yet "instantly familiar", there will also be a series of functionality updates.

Key features include a new control centre and overhauled notification centre, an updated camera app, the addition of Airdrop for iPhone, and improved app to app jumping. Siri will now include Twitter and Facebook integration, have the option of a male voice and be able to change the phone's settings.

iPhone users will also finally be able to block numbers on phone, messages and FaceTime, a setting that has been conspicuously missing from previous versions of iOS.

As well as a new look Safari with true full screen browsing, the app will have a new privacy option called 'do not track', an update on the 'private browsing' function of iOS 6.

For a closer look at some of the most overlooked iOS 7 features, head over the our guide.